J.H. De Ridder

Factor analysis of possible risks for hypertension in a black South African population

To date only a small number of studies have investigated the pattern of associations within a set of hypertension risks. The objective of this study was therefore to examine the interrelation of main hypertension risks in an African population by using factor analysis in order to detect underlying risk patterns. Subjects aged 16–70 years (N=963) were recruited from 37 randomly selected sites throughout the North West Province during 1996–1998. Exclusion criteria were pregnancy, lactation, casual visitors, drunkenness and treatment for chronic diseases, such as hypertension. Subjects with blood pressures exceeding 140/90 mmHg were classified as hypertensive. Children aged 10–15 years were also recruited from 30 randomly selected schools during 2000–2001 (N=694). Children were classified as hypertensive when an average systolic or diastolic blood pressure greater than or equal to the 90th percentile for age and sex was encountered, while correcting for height. The following hypertension risks were measured: urbanisation, obesity, plasma fibrinogen, lipids, insulin, serum gamma glutamyl-transferase, dietary intake, smoking and alcohol consumption.From 23 risks the factor analysis disclosed five factors that explained 56.2% of the variance in the male and 43.5% of the variance in the female group: an urban malnutritional phenomenon, the metabolic syndrome X, a hypercholesterolaemic and obesity complex, an alcoholic hypertriglyceridaemia, and central and peripheral cardiovascular hypertensive effects. In conclusion, South Africans migrating from rural to urban areas adapt to a new lifestyle with numerous risks, resulting in conditions like malnutrition, the metabolic syndrome X, dyslipidaemia, alcoholism, obesity and increased peripheral vascular resistance. For successful prevention of hypertension in a population in transition, a whole risk pattern should be corrected, rather than an individual risk by implementing lifestyle modification programmes.

Dietary risk markers that contribute to the aetiology of hypertension in black South African children: the THUSA BANA study

Although clinical hypertension occurs less frequently in children than in adults, ample evidence supports the concept that the roots of essential hypertension extend back to childhood. Since little is available in the literature on causal dietary factors of hypertension in children, this study hypothesised that certain dietary factors can be identified as risk markers that might contribute to the aetiology of hypertension in black children. Children aged 10–15 years were randomly selected from 30 schools in the North West Province from 2000 to 2001. These children comprised 321 black males and 373 females from rural to urbanised communities, of which 40 male and 79 female subjects were identified with high-normal to hypertensive blood pressure. Blood pressure was measured with a Finapres apparatus and data were analysed with the Fast Modelflo software program to provide systolic, diastolic and mean blood pressure. A 24-h dietary recall questionnaire and weight and height measurements were taken. In a stepwise regression analysis, the following variables were significantly associated (P⩽0.05) with blood pressure parameters of hypertensive males: biotin, folic acid, pantothenic acid, zinc and magnesium. Energy, biotin and vitamin A intakes were significantly associated with blood pressure parameters of hypertensive females. No significant dietary markers were indicated for any of the normotensive groups. Dietary intakes of all of these nutrients were well below the dietary reference intakes. In conclusion, the dietary results coupled with the cardiovascular parameters of this study identified folic acid and biotin as risk markers that could contribute to the aetiology of hypertension in black persons. The low intakes of these nutrients, among others, is a matter of serious concern, as is the increasing tendency towards urbanisation.

Determining ethnic-, gender-, and age-specific waist circumference cut-off points to predict metabolic syndrome: the Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA) study

Abstract Objective: The aim was to determine receiver-operating characteristic (ROC) waist circumference (WC) cut-off points best associated with metabolic syndrome (MetS) in a cohort of South African teachers. Design: Target population study. Setting and subjects: Four hundred and nine urban black (Africans) and white (Caucasians) from the Kenneth Kaunda district in North West province, between the ages of 25 and 65 years old, were stratified according to gender and age (25–45 years and 46–65 years). Outcome measures: Anthropometric, fasting overnight urine and biological markers for MetS. Results: ROC analysis determined pathological WC cut-off points of 91 cm for African men and 84 cm for African women. It is recommended that WC cut-off points should be 97 cm for Caucasian men and 84 cm for Caucasian women. Pathological WC cut-off points significantly predicted MetS in all ethnic-, gender- and age- specific groups, especially in male groups, with odds ratios of 7.6 [95% confidence interval (CI): 3.4–17.1, p-value = 0.00) for African men and 6 (95% CI: 3–12.1, p-value = 0.00) for Caucasian men. Conclusion: ROC-developed WC cut-off points were found to be good predictors of MetS in a South African cohort, especially in the men. Further research in prospective cohort studies is warranted to verify our findings.

Structural vascular disease in Africans: performance of ethnic-specific waist circumference cut points using logistic regression and neural network analyses: the SABPA study

A recently proposed model for waist circumference cut points (RPWC), driven by increased blood pressure, was demonstrated in an African population. We therefore aimed to validate the RPWC by comparing the RPWC and the Joint Statement Consensus (JSC) models via Logistic Regression (LR) and Neural Networks (NN) analyses. Urban African gender groups (N=171) were stratified according to the JSC and RPWC cut point models. Ultrasound carotid intima media thickness (CIMT), blood pressure (BP) and fasting bloods (glucose, high density lipoprotein (HDL) and triglycerides) were obtained in a well-controlled setting. The RPWC male model (LR ROC AUC: 0.71, NN ROC AUC: 0.71) was practically equal to the JSC model (LR ROC AUC: 0.71, NN ROC AUC: 0.69) to predict structural vascular -disease. Similarly, the female RPWC model (LR ROC AUC: 0.84, NN ROC AUC: 0.82) and JSC model (LR ROC AUC: 0.82, NN ROC AUC: 0.81) equally predicted CIMT as surrogate marker for structural vascular disease. Odds ratios supported validity where prediction of CIMT revealed -clinical -significance, well over 1, for both the JSC and RPWC models in African males and females (OR 3.75-13.98). In conclusion, the proposed RPWC model was substantially validated utilizing linear and non-linear analyses. We therefore propose ethnic-specific WC cut points (African males, ≥90 cm; -females, ≥98 cm) to predict a surrogate marker for structural vascular disease.

Association of waist circumference with perception of own health in urban African males and females: the Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA) study

Abstract Background: Current waist circumference (WC) cut-points of the Joint Statement Consensus (JSC) (male ≥ 94 cm, female ≥ 80 cm) were compared with a recently proposed WC cut-point (RPWC) (male ≥ 90 cm, female ≥ 98 cm). In this study, we aimed to compare the two cut-points to assess the association between central obesity and perception of own health. Method: We determined blood pressure and fasting bloods [glucose, high-density lipoprotein (HDL) and triglycerides] as metabolic syndrome markers for 171 urban teachers. Perception of own health was determined via the General Health Questionnaire-28 (GHQ-28) to indicate probable psychological distress or a psychiatric disorder or caseness (≥ 4). Results: The RPWC was an improved discrimination between the WC groups on perception of own health as reflected in the GHQ-28 subscales. In the male group, higher scores were found in the RPWC high WC group (≥ 90 cm) with regard to somatic symptoms, social dysfunction and GHQ-28 caseness, compared to those of the low WC groups (< 90 cm). Compared to the RPWC high WC females (≥ 98 cm), the low WC (< 98 cm) reflected significantly higher anxiety and sleeplessness subscale scores. Conclusion: Our results suggest that the RPWC (men 90 cm, women 98 cm), (determined in this African cohort when adding GHQ-28 caseness as a discriminatory variable between WC cut-point), distinguished better between WC groups based on their perception of own health than the JSC cut-point.

The association between seven-day objectively measured habitual physical activity and 24 h ambulatory blood pressure: the SABPA study

Few studies have examined objective physical activity in relation to 24 h ambulatory blood pressure (BP). We aimed to assess the association of 7-day objectively measured habitual physical activity with ambulatory BP in a sample of African and Caucasian school teachers (n=216, age 49.7 years) from the sympathetic activity and blood pressure in Africans prospective cohort study. Hypertension (ambulatory systolic BP⩾130 and/or diastolic BP⩾80 mm Hg) was prevalent in 53.2% of the sample, particularly in black Africans. The hypertensive group spent significantly more awake time in sedentary activity (51.5% vs 40.8% of waking hours, P=0.001), as well as doing less light- (34.1% vs 38.9%, P=0.043) and moderate-intensity (14.0% vs 19.7%, P=0.032) activities compared with normotensives, respectively. In covariate adjusted models, light-intensity activity time was associated with lower 24 h and daytime ambulatory systolic BP (β=−0.15, 95% confidence interval (CI): −0.26, −0.05, P=0.004; β=−0.14, CI: −0.24, −0.03, P=0.011) and diastolic BP (β=−0.14, CI: −0.25, −0.03, P=0.015; β=−0.13, CI: −0.24, −0.01, P=0.030), as well as resting systolic BP (β=−0.13, CI: −0.24, −0.01, P=0.028). Sedentary time was associated only with 24 h systolic BP (β=0.12; CI: 0.01, 0.22), which was largely driven by night-time recordings. Participants in the upper sedentary tertile were more likely to be ‘non-dippers’ (odds ratio=2.11, 95% CI: 0.99, 4.46, P=0.052) compared with the lowest sedentary tertile. There were no associations between moderate to vigorous activity and BP. In conclusion, objectively assessed daily light physical activity was associated with ambulatory BP in a mixed ethnic sample.